Propeller mechanism



Oct. 7, 195a T. BARISH Em, 2,855,055

PROPE'LLER MECHANISM Original Filed Aug. 27, 1952 5 Sheets-Sheet 1 Oct. 7, 1958 T. BARISH ET AL 2,855,055

PRQPELLER MECHANISM Original Filed Aug. 27, 1952 5 Sheets-Sheet 2 IN V EN T ORJ' BY CLIFFORD a. nae/ #7 m, Mean/ 4 rra/elvi rs TfBARIs'H Y EflAL PROPELLER MECHANISM Oct. 7, 1958 Original Filed Aug. 27, 1952 s Sheets-Shet 3 y CLIFFOED a 4/444, 4444... 1,1

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w Tw a M020 r N #w r 2 awe A-rroezveys I llllllli United States Patent PROPELLER MECHANISM Thomas Barish, Cleveland, John D. Moeller and Robert C. Treseder, Dayton, and Clifford B. Wright, Tipp City, Ohio, assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Original application August 27, 1952, Serial No. 306,704. and this application October 6, 1955, Serial No.

3 Claims. (Cl. 170-135.75)

The present invention relates to variable pitch propellers and more particularly to mechanism for adjusting the pitch position of propeller blades.

This is a divisional application of copending parent application S. N. 306,704, filed August 27, 1952, now Patent No. 2,797,761.

Among our objects are the provision of a propeller hub embodying unitary torque unit means for effecting concurrent pitch adjustment of all propeller blades journaled within the hub, and the further provision of such fluid pressure actuated torque unit means that are selflocking in the absence of fluid pressure.

The aforementioned and other objects are accomplished in the present invention by providing a fluid pressure actuated stepping motor within the propeller hub, which stepping motor is operatively connected with each of the several propeller blades rotatably journaled therein. Specifically, the propeller hub assembly is supported for rotation about a fixed hollow shaft. The hollow shaft is supported by a stationary spider that is anchored to non-rotatable aircraft structure. The propeller hub is driven through a compact gear reduction unit including gearing mechanism which effects rotation of the propeller in a direction opposite to that of the prime mover whereby the large gyroscopic effects oppose each other. A fluid pressure regulator is supported fore the propeller hub, as is a brush and slip ring assembly. Valve means within the rotatable regulator control the application of fluid medium under pressure to the stepping motor for effecting adjustment of the blade pitch positions. In addition accumulator chambers are provided within blade supporting spindles of the hub structure, the chambers having connection with pressure developing means disposed within the regulator.

The stepping motor includes and internally toothed ring gear having three transversely extending openings disposed substantially 120 apart. Within each opening, crank pins are rotatably journaled, the crank pins having oppositely extending eccentric pintles which are journaled in plate members. Also journaled on the crank pins are crank arms that are operatively connected to pistons. The pistons are disposed for reciprocal movement within cylinders, which movement is effected by fluid under pressure. The preceding motor structure is mounted eccentrically with respect to the axis of propeller rotation. Disposed within the internally toothed ring gear, and having only one or two adjacent teeth at a time in load engagement therewith, is a sleeve provided with a pair of axially spaced toothed portions. The sleeve is journaled for rotation about the propeller axis. The teeth of the sleeve and the ring gear differ by three, with the former having the lesser number of teeth. The second toothed portion of the sleeve engages a plurality of planet gears, which in turn are drivingly connected with a plurality of worm shafts associated with the pro peller blades. The entire stepping motor assembly rowhen pitch adjustments are being effected.

The valve means within the hub direct fluid pressure sequentially to the stepping motor cylinders, and the order of the sequence determines the direction of ring gear movement relative to the propeller hub. This circular translatory movement is transmitted to the toothed sleeve member, which, in turn, efiects movement of the propeller blades through irreversible gear trains. The stepping motor by reason of its eccentric disposition is self-locking in the absence of fluid pressure application thereto.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention Will be clearly shown.

In the drawings:

Figs. 1 and 2 combined represent a longitudinal sectional view of the propeller hub and its associated gear reduction unit.

.Fig. 3 is a view taken along line 33 of Fig. 2 with certain parts removed.

Fig. 4 is a view taken along line 3-3 of Fig. l with certain partsremoved and including fragmentary sec tional details.

Fig. 5 is a perspective view, in part exploded, of the stepping motor assembly.

Fig. 6 is a schematic diagram of a control system which may be utilized to effect control of the stepping motor.

Referring more particularly to Figs. 1 and 2 combined, propeller hub structure 1 is supported by a bearing means 2upon a fixed hollow shaft 3. The fixed hollow shaft 3 is, in turn, supported by stationary parts of a gear reduction unit 4 that are, in turn, rigidly connected to nonrotatable, rigid portions of the aircraft. Concentrically disposed within a sleeve 5 is a prime mover driven assembly 6. The assembly 6 is splinedly connected at 7 to a shaft of a drive gear 8. The shaft of the drive gear 8 is rotatably supported by bearing means 9 within the gear reduction unit housing 4. The gear 8 meshes with four planet gears, only one, 10, of which is shown. The planet gears mesh with a stationary internal ring gear 11, which is attached to a sleeve that splinedly engages stationary portions 13, 14 and 15 of the gear housing 4. The planet gears, of which 10 is one, are journaled on pins 16, which are attached to a spider or carrier 17 by screw devices. is rotatably journaled by hearing means 29 and 29a within the portion 13 of the gear housing. The carrier is also splinedly connected at 18 to a sleeve 19 which, in turn, drives a ring gear 20. Meshing with the ring gear 20 are a plurality of pinion gears 21, only one of which is shown. The pinion gears 21 may be used to drive accessories, such as tachometers, generators or alternators. The carrier 17 is also splinedly connected at 22 to a pinion gear 23. The planetary gear set aforedescribed is merely utilized for gear reduction purposes and forms no part of the present invention.

Referring to Figs. 1 and 3, the pinion 23 meshes with four idler gears 24, which are supported by hollow pins 124 and rotatably journaled thereon by bearing means 125 within openings formed in a radially inwardly extending part of the stationary portion 13. The radially inwardly extending part forms a stationary spider 113- through which the fixed shaft 3 is supported. The stationary portion 13 is connected by any suitable means to any nonrotatable aircraft structure, not shown. The stationary spider 113 is also provided with a plurality of openings 126 for weight reduction purposes. A conduit 127, which isutilized to carry control leads, not shown, to the hollow shaft 3, extends through one of the openings 126. The four idler gears 24 mesh with an internal Patented Oct. 7, 1958 The carrier 17 ring gear 25. The internal ring gear 25 is provided with a flange 26 which is splinedly connected at 27 to a flange 28 provided by the hub structure 1. As the prime mover may take the form of a turbine, and as both the turbine and the'propeller have large moments of inertia, means are provided for effectingrotation of these units in opposite directionsto facilitate the balancing out of the two gyroscopic effects. This reversal of rotation between the turbine driven assembly6 and the propeller hub 1 is effected through. the gear set including pinion 23, idlers 24, andring gear 25. Moreover, plural power paths are provided between the gear 23 and the ring gear 25, which is connected with the hub 1, by the four idler gears 24 which'are journaled within the fixed spider 113. In addition, thestationary spider. 113 supports the fixed hollow shaft 3 by reason of the flanged connection therebetween.

Referringmore particularly to Figs. 1, 4 and 5, the propeller hub structure 1, which is driven by and supported through a compact gear reduction unit aforedescribed, will nowbe dealt with in detail. The propeller hub structure 1 is provided with four radially extending spindles 30, one of which is shown in Fig. 1. The spindles are disposed 90 degrees apart and are of hollow construction. Coaxially disposed about each of the hollow spindles are the hollow shanks of propeller blades. As is shown in Fig. 1, the hollow shank portion 31 of a propeller blade 32 is supported for movement about its longitudinal axis about the spindle 30 by stacked bearing means 33 and radial bearing means 34. The inner raceways of the stack bearings 33 are formed integral with the outer circumferential surface of the spindle 30. The outer races 39 of the stack bearings 33 are interposed between an annular member 36 and a hollow sleeve 37. The annular member 36 is provided with a flange 38, which engages an internal shoulder 39a formed on the internal surface of the shank 31. The sleeve 37 is maintained between the outer races 39 of the stacked bearing 33 and the outer race of the radial bearing 34 by means of a plurality of bolts 40, which engage ring 34a forming the outer raceways of bearings 34 and threadedly engage the shank portion 31 of the propeller blade. The centrifugal thrust of the blades is transmitted through the sleeves 37 to the stacked bearings 33. Each of the propeller blades 32 has secured to the blade shank end thereof a worm gear 41. The worm gears 41 are disposed to engage worm wheels 42, which are fixed to worm shafts 43, as is shown in Figs. 4 and l. The worm wheels 41 are journaled for rotation within the propeller hub structure 1 by hearing means 44. The bearing means 44 are supported by a cover structure 45, which is anchored to the propeller hub 1 by screw devices 46.

Referring to Fig. l, the worm shafts 43 are journaled by hearing means 47 and 48 in tubular portions 49 of the cover structure 45. One end of the cover structure 45 is flangeconnected at 50 to a plate member 51 which forms one wall of a fluid pressure regulator designated generally by 52. Disposed between the plate 51 and the spindles 38 is a stepping motor type torque unit means 53.

Referring particularly to Fig. 5, the component parts of the stepping motor assembly 53 will be described in detail. The stepping motor includes an internally toothed ring gear 54. The ring gear 54 forms part of a toroid, which includes inner and outer rim members 56 and 57 that are integral with pairs of arcuate members 58 and 59, 60 and 61, 62 and 63, which pairs are disposed substantially 120 apart. Each pair of arcuate members provides a circular opening within which are mounted roller bearing assemblies 64, 65 and 66. Journaled within roller bearing assembly 64 is a crank pin 67 and, likewise, journaled within roller bearing assemblies 65 and 66 are crank pins 68 and 69, respectively. The crank pin 67 is provided with oppositely extending eccentric pintle portions 70 and 71.- The crank pins 68 and 69 are, likewise, provided with oppositely extending eccentric pintle portions. Rotatably journaled on the crank pin 67 is a crank arm 72, the crank arm being operatively connected with a piston 73. The piston 73 is adapted for reciprocal movement within a cylinder 74. In a like manner, a crank arm 75, connected withua piston 76, is rotatably journaled on the eccentric pin 68, as is crank arm 77 and its piston 78 associated with crank pin 69. The pistons '76 and 78 are each mounted for reciprocal movement within separate cylinders, not shown in Fig. 4. Referring again to Fig. l, the cylinder 74 is shown rigidly attached to the plate 51. The cylinders which are associated with pistons 76 and 78 are likewise disposed within the propeller hub structure. Eccentric pintle 70 of the crank pin 67 is rotatably journaled by a bearing means within the plate 51. The eccentric pintle 71 of the crank pin 67 is rotatably journaled by hearing means in a second plate '79, which is suitably attached to the rotating propeller hub 1. Disposed within-the hollow bore 80 of the hub 1 and flange connected thereto at 81 is a stepped sleeve member 82. The stepped sleeve member 82 is provided with a plurality of passages, one, 83, of which is shown in Fig. l, the purpose of which will be later described. Rotatably journaled by bearing means 84 and 85 upon the sleeve 82 is a second sleeve 86 having axially spaced externally toothed portions 87 and 88.

Referring again to Fig. 5, toothed portion 87 of the sleeve 86 is adapted for engagement with the internally toothed ring gear 54 of the toroid assembly 55. The parts are so constructed that the number of the teeth on portion 87 of the sleeve are three less than appear on the internally toothed ring gear 54. Thus, with the toroid assembly 55 eccentrically mounted with respect to the axis 89 of propeller rotation, while the sleeve 86 is journaled for rotation about the axis 89, each circular translatory movement of the toroid 55 will rotate the sleeve 86 throughout an arcuate distance of three teeth. In this manner, automatic gear reduction between the toroid 55 and the sleeve 86 is obtained. Moreover, the parts are so arranged that the load is transmitted between ring gear 54 and toothed portion 87 through only one or two adjacent teeth at a time.

Referring again to Fig. l, the externally toothed portion 88 of the sleeve 86 meshes with a planet gear 98, which is rotatably journaled by bearing means 91 within a radially inward extension of the cover assembly 45. Four planet gears are provided and each of the planet gears mesh with a pinion gear 92, which is anchored to-one end of the worm shaft 43. The sleeve 86 is maintained in position upon the sleeve 82 by means of a ring 82a, which threadedly engages an external portion of the sleeve 82.

During rotation of the propeller, the entire assembly, except for fixed shaft 3, rotates. By reason of the three crank pins of the stepping motor being united through the toroid 55, they effectively act as the three throws of a crank shaft, the throws being displaced Moreover, the toroid 55 can only be moved in a circular translatory path about the crank pin axes through sequential actuation of the pistons associated with the crank pins. If the fluid pressure system or the control system therefor fails, the toroid will automatically leek at dead center position at any one of the crank pins. Accordingly, the torque unit is self-locking upon any malhm':- tionoccurring in the control system. This, in effect, constitutes an automatic pitch lock for the propeller blade.- durlng the absence of fluid pressure application to the stepping motor piston and cylinder combination. To etfect adjustment in the pitch position of the blades the toroid assembly 55 must be moved relative to its associated rotatable structure including plates 51 and 79.

To etfect relative movement between the toroid 55 and the plates 51 and 79, fluid pressure must be applied in a predetermined sequence to the cylinders associated with pistons 73, 76 and 78. For instance, if fluid pressure is first applied to cylinder 74, a radially inward movement of the piston 73 to the dead center position of the crank pin 67, followed by inwardly radial movement of pistons 76 and 78 in that order will effect a movement of the toroid assembly 55 about the axes of the crank pins relativeto the plates 51 and 79. This circular-translatory motion of the assembly 55 will effect an arcuate movement of the sleeve 86 through toothed engagement between gear portions 87 and 54. Arcuate movement of the sleeve 86 will be transmitted through toothed portion 88, planet gears 90, pinion gears 92 to the worm shafts 43, which through the worm gear 42 will effect rotative movement of the worm wheels 41 that are operatively connected to the propeller blades 32. In this manner, each of the several propeller blades will be moved through exactly the same angular distance whereby concurrent pitch adjustment is effected.

Disposed within each of the hollow spindles 30 is a free piston 93, which divides the hollow spindles into a gas chamber 94 and a hydraulic fluid pressure chamber 95. The chamber 94 is closed at its outer end by a head member 194. The piston 93 is centrally apertured at 96 and is adapted to slide along the surface of a transfer tube 97, which is secured at its inner end to a tubular nut 97a having threaded engagement with a boss formed on the hub structure 1. Passage 83, within the stepped sleeve 82, communicates with a pocket 98, which, in turn, communicates with the'transfer tube 97 to provide means for'admitting gas under pressure to the chamber 94. Chamber 95 is connected by a bore 99 to a pocket 100 within the sleeve 82 which is connected by a passage, not shown, in the sleeve 82 to a passage within the plate 51 for supplying fluid medium under pressure to the chambers 95. The connecting passages between the hollow spindles and the plate 51 are similar to those shown in the Blanchard et al. Patent 2,307,102. Thus, it is seen that the hollow spindles 30 may be usedto provide accumulator chambers for the storage of hydraulic fluid medium under pressure.

A regulator cover 101 is supported by bearing means 102 upon the fixed shaft 3. Attached to the cover 101 is a slip ring assembly 103. Attached to the end of shaft 3 is a brush assembly 104, which cooperates with the slip ring assembly 103. Leads for conducting electric energy to the brush assembly 104 are disposed within the hollow shaft 3. The brush and slip ring assembly is enclosed by a cover 105, which is flange connected to the regulator cover 101. Connection between the several slip rings and the interior of the regulator 52 is accomplished by terminal structure such as is shown at'106. The terminal structure includes a pin 107, which engages a slip ring at one end, the other end of the pin engaging a spring contact 108, which is insulatingly supported on the cover 101. The spring contact 108 is, in turn, connected by a terminal stud 109 to the interior of the regulator 52. Mounted within the regulator 52 and restrained from rotation by means of the fixed shaft 3 is an externally toothed gear 110. The gear 110 may be used to operate a system pump for developing fluid pressure in a manner similar to that disclosed in the aforementioned Blanchard et al. patent. Disposed within the regulator 52 and attached to the plate 51 are the several elements of a fluid pressure control system for effecting movement of the pistons associated with the stepping motor.

Referring to Fig. 6, a schematic control system for the instant propeller is shown. The control system is by way ofexample and not by way of limitation. The fluid pressure control-circuit includes a pump 111, which may be driven by relative-rotation between the power gear 110 and the regulator plate'51. The gear type pump 111 has an inlet at 112, which communicates with the reservoir formed by members 101 and 51, which sealingly engage the fixed shaft 3. The output of the pump 111 flows through a check valve 213 and into a high pressure trunk line 114. Pressure in the trunk line 114 is controlled by a pressure relief valve 115. The trunk line 114 communicates with the supply ports of three solenoid actuated valves 116, 117 and 118. As all of the valves are of identical construction, a detailed description of one is deemed to be sufficient. Solenoid actuated valve 116 includes a valve guide 119 having a supply port 120, a drain port 121 and a distribution port 122. The supply port is connected to the trunk line 114, the distribution port is connected by line 123 to cylinder 74 of the stepping motor. Disposed within the valve guide 119 is a plunger 224, normally centered by a pair of springs 228 and 229, having a pair of spaced lands 225 and 226. One end of the plunger is provided with an armature 227, which is encompassed by solenoid winding 128. Each of the solenoid valves is so constructed that during solenoid winding deenergization, the lines 123, 129 and 130, which lead to the stepping motor cylinders '74, 131 and 132, respectively, are connected to drain. During energization of solenoid windings 128, 133 and 134, the lines 123, 129 and 130, respectively, are connected through the supply ports to the trunk line 114. One end of each of the solenoid windings 128, 133 and 134 is connected to ground by a common conductive line 135. The other ends of windings 128, 133, 134 are connected, respectively, by conductive lines 136, 137 and 138 to slip rings 139, 140 and 141. Slip rings 139, 140 and 141 are, respectively, contacted by brushes 142, 143 and 144. The brushes 142, 143 and 144 are, in turn, connected by electric lines to means for sequentially energizing the solenoid windings 128, 133 and 134 to effect substantially constant speed propeller operation. Structurally, the brushes 142, 143 and 144, and the slip rings 139, 140, and 141, form part of the brush and slip ring assembly 103, 104 shown in Fig. 1.

The control means for sequentially energizing the solenoid windings 128, 133 and 134 includes an electronic discriminator circuit. This circuit comprises a standard signal source in the form of a stable adjustable single phase A. C. generator 244 and a three-phase alternator including an armature 223 with a stator winding 230". The armature 223 is driven at a speed proportional to the speed of rotation of propeller hub 1 and produces signals displaced 120 electrical degrees apart on the windings of stator 230. Accordingly, the frequency of the three phases appearing on the windings of stator 230 is proportional to the speed of rotation of the hub 11. The frequency of the single phase A. C. generator 244 may be varied by adjustment of element 148, which, in effect, forms a pilots speed control. This signal generator produces an A. C. voltage between conductor 149 and ground 146, the frequency of which is dependent upon the pilot control adjustment 148. This signal is impressed on the conductor 149 from which it is simultaneously impressed on grids 238, 240 and 242 of thyratron tubes V1, V2 and V3 by means of'conductor 150. The tubes V1, V2 and V3 include plates 184, 186 and 188; screen grids 172, 174 and 176, the control grids 238, 240 and 242, cathodes 166, 168 and 170 and filaments 196, 198 and 200. The filaments are energized in series by a voltagedivider network including resistance 206 and are connected between conductors 202 and 204 between the terminals of a D. C. power source 300.

The three phases, 120 electrical degrees apart, that are developed by the armature in the windings of stator 230 are sequentially impressed upon the plates 184, 186 and 188 of the thyratrons V1, V2 and V3 by means of conductors 326, 328 and 330, respectively. Thus, the tubes are given a positive plate potential in sequence, 120 electrical degrees apart. However, the control grids 238, 240 and 242 of these tubes that are simultaneously impressedwith asignal from the generator 244 which, when positive, places all three tubes in a conductive condition. Accordingly, each of the tubes will conduct whenever both its plate and grid have positive potentials of correct magnitude impressed thereon coincidentally. It may therefore be seen that only one tube will conduct at a time. The screen grids 172, 174 and 176 are directly connected to the cathodes 166, 168 and 170. The cathode circuit of tube V1 is through a relay coil 378, the energization of which effects movement of armature 218 of the relay away from contact 232so as to close with contact 234. This energization takes place whenever the tube V1 conducts. The cathode circuit of V2 is similarly connected through relay coil 38%, which controls armature 220, and the cathode circuit of tube V3 is likewise connected through relay coil 332 which controls armature 222. As each of the circuits associated with the relay armatures are alike, a description of one is deemed to be sufficient. The relay circuits include a pair of contacts 232 and 234 with the armature disposed therebetween. The contacts 234 are connected by a conductive line 21% with the power source 300. inserted between the armature and the conductive line 21% is a rectifier 214, which is used for arc suppression at the relay contacts. Contacts 232 are similarly connected with rectifiers 216 to a conductive line 212 and ground. The armatures 218, 224 and 222 connect by lines 231, 233 and 235 to the brushes 142, 143 and 144.

In operation the three-phase signal of the alternator is balanced against the single phase master signal by means of the discriminator circuit to produce a control signal depending upon the relative frequency difference between the signal generator 244 and the alternator windings 230. This control signal is used to adjust the load on the engine propeller combination so as to increase or decrease the speed thereof, which, in turn, increases or decreases the frequency of the alternator so that the alternator signal and the reference generator signal are brought into synchronism, which represents an onspeed condition.

Operation This counterclockwise movement of gear 54 will, in turn,

effect counterclockwise movement of ring gear 87 which, through its transmission, will effect an increase in the pitch position of the blades 32 in an effort to correct the overspeed condition. When the propeller speed returns to the preselected level, the energization of tubes V1, V2

and V3 will be such that positive pulses coincide in only i one of the tubes. Likewise, only one and the same solenoid winding will be sequentially energized and deenergized. However, reciprocal movement of only one of the pistons cannot cause circular translatory movement of the toroid assembly 55 due to dead centering of the crank pins during movement of the pistons. Thus, the periodical reciprocal movement of one of the pistons will not effect movement of the toroid assembly 55. If the propeller speed should be less than the selected speed, the tubes will conduct in the sequence V3, V2, V1, thereby effecting clockwise circular translatory movement of the toroid 55 and a consequent movement of the propeller blades to a lesser pitch position.

While the embodiment of the present invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. Assembly structure for variable pitch propeller mechanism comprising, a power plant driven shaft, a reduction gear housing, a single piece support member fixed to said housing, a hollow stationary shaft attached to said member, a propeller hub rotatably journalled on said shaft, a plurality of variable pitch propeller blades adjustably mounted on said hub, pitch changing means carried by the hub and operatively connected with said blades, control means for said pitch changing means, a conduit in said support member adapted for accommodating actuating means for said control means through said hollow shaft to said control means, and a compact gear reduction unit inside said housing including therein a pinion gear in driving relation through a plurality of idler gears meshing with an internal ring gear thereby operatively engaging said power plant driven shaft to effect rotation of said propeller hub in a direction opposite to the shaft, said opposite rotation cancelling gyroscopic forces so that vibratory stresses are avoided leaving only bending stresses on said hollow stationary shaft.

2. In combination with a gear reduction means between a turbine driven shaft and a rotating propeller hub, a plurality of variable pitch propeller blades adjustably mounted on said hub, means for varying propeller pitch including a regulator mounted with said hub, a gear reduction housing, a fixed spider rigidly attached to said housing, a hollow shaft non-rotatably attached to said spider, control means for said regulator disposed on said shaft, a conduit in said spider providing a path for control leads through said hollow shaft to said control means, said propeller hub being rotatably journalled on said shaft, an internal ring gear drivingly connected to said hub, a plurality of idler gears meshing with said ring gear rotatably disposed thereto on said fixed spider, a pinion gear for rotating said idler gears, a carrier operatively engaging said pinion gear with said gear reduction means to effect rotation of said propeller hub in a direction opposite to rotation of said turbine driven shaft facilitating the balancing out of the two gyroscopic effects.

3. In a propeller installation having a rotating drive turbine, a turbine driven shaft rotating in one direction causing a gyroscopic force effect in one direction, a rotatable propeller hub separate from said shaft, a fixed memher about which said hub rotates, a plurality of propeller blades mounted on said rotatable hub causing therewith a gyroscopic force effect in opposing direction relative to that of said turbine driven shaft, pitch changing means carried by said hub and operatively connected with said blades, control means for said pitch changing means, said fixed member being hollow and usable as a fixed conduit for a non-rotating connection transmitting actuation between said control means and said pitch changing means, a gearing mechanism interconnecting said turbine driven shaft and said hub, said gearing mechanism including a pinion gear with said shaft, a plurality of idler gears in toothed engagement therewith, a stationary spider with said fixed member and rotatably journalling said idler gears, and an internally toothed ring gear drivingly attached with said hub, said idler gears constituting a plurality of power paths between said turbine driven shaft and said hub effecting opposite directional rotation thereof relative to each other whereby the gyroscopic effects oppose each other leaving only bending stresses rather than vibratory stresses on said hollow fixed member serving as the aforesaid conduit.

References Cited in the file of this patent UNlTED STATES PATENTS Petrie Dec. 8, 1953 

